I stuck with Kafka because I respected The Metamorphosis when I read it at university and I haven't read anything else he's written.

However, to be honest, all three options sound pretty interesting to me. I've never bothered with Dunsany, but this might be a good intro to his writing and I can't see how you could go wrong with Hemmingway.

I decided to purchase The Complete Short Stories of Ernest Hemingway : The Finca Vigia Edition published by Simon & Schuster in the US. It includes "The First Fourty-Nine" plus 21 other stories. Finca Vigia (Lookout Farm) was his home in San Francisco de Paula, Cuba where he lived on and off for 2 decades. It has a very short foreword by his sons. Wikipedia has a great synopsis about this collection.